1. Field of the Invention
This invention relates to a spindle control system for stopping a spindle of a machine tool at a predetermined position.
2. Description of the Prior Art
In a machine tool, there are some occasions when a turning operation is followed by milling, punching or the like, which requires that the work mounted on the spindle be positioned at a desired rotational angular position. To perform this, control of the spindle includes both rotation control for the turning operations and position control for positioning the spindle at the desired rotational angular position.
With a conventional spindle control system, both a motor for turning operations and a motor for positioning are used. To position the spindle at a desired rotational angular position, the spindle is brought, under the control of the positioning control, to a specific position where a specific rotational position signal is obtained. The spindle is then positioned at a commanded angular position under the control of the positioning motor.
This prior art method employs, in combination, a detector for producing the specific position signal at the specific rotational position (for example, an original position) of the spindle and a resolver or like detector coupled with the positioning motor to detect its rotational angle. With this method, however, the current position of the spindle at every moment is not available, so that when shifting from turning operations to the positioning control, it is necessary to stop the spindle once at the aforesaid specific position and then to re-start the positioning motor to accomplish the positioning control using a rotational position command and a feedback signal from the resolver. Accordingly, the conventional method has the defect that the spindle cannot be rapidly positioned at a commanded position.